Solid adducts of lanthanide nitrates and chlorides with diisopropyl-N,N-diethylcarbamylphosphonate were prepared and studied. The La, Ce, Pr, Nd, Sm, Gd, and Tb nitrate adducts were isolated and shown to have the structure ▪ The Dy, Er, Ho, and Yb nitrate adducts were difficult to isolate and were found to have no single, discrete structure. The chloride adducts of La, Pr, Sm, and Tb were isolated and assigned the structure ▪